Metal bladders for positive expulsion tanks or like product storage devices are presently well known in the art. As by way of example, U.S. Pat. No. 3,275,193 discloses a product storage container, wherein a cup-shaped diaphragm or bladder is formed of a malleable material, such as aluminum, steel, nickel, etc., which is capable of cold flow incremental rolling bending movement to a substantially permanent plastic deformation. A rim portion of the cup-shaped diaphragm is secured to the juncture of a pair of cup-shaped shell portions, which cooperate to define a container or tank divided by the diaphragm into two compartments or chambers. Product stored in one of these compartments may be expelled from the container by means of a pressurized gas introduced into the other compartment; the difference in pressure across the diaphragm serving to effect rolling of the diaphragm upon its self to eventually assume an inside out or inverted configuration incident to essentially complete expulsion of the product from the container. With a diaphragm construction of the type disclosed in this patent, it is critical that the diaphragm be designed to "roll" at a pressure less than the pressure at which the diaphragm will be subject to buckling deformation, such as would otherwise result in failure of the diaphragm and/or the trapping of product within the container.
Prior attempts to insure proper roll deformation of expulsion tank and like diaphragms have principally led to "geometric" solutions of the buckling problem, including increasing the side wall thickness of the diaphragm, reducing the length to diameter ratio of the diaphragm, sloping or curving the side walls of the diaphragm and/or reinforcing the side walls of the diaphragm by providing separate reinforcement elements or forming such side walls with undulating folds or as a series of stepped diameter cylinders, as discussed for instance in U.S. Pat. Nos. 3,275,193 and 3,494,513.
Reference is also made to U.S. Pat. No. 3,711,027, which discloses an extendable nozzle for rocket engines, which was fabricated to a frusto-conical configuration and then partially telescopically rolled upon itself to provide a nozzle having a reduced longitudinal dimension in its "stowed" condition.
As with rolling expulsion diaphragms of the type disclosed in U.S. Pat. No. 3,494,513, it was the practice to subject the fabricated nozzle to an annealing operation in order to remove stresses introduced into the diaphragm material during fabrication with a view towards reducing rolling, ie. gas deployment, pressure to a minimum. As a practical matter, it was found necessary to provide the nozzle with a rolling guide or filler boundary in order to avoid buckling failure of the nozzle within acceptable ranges of the ratios "D"/"t" and "L"/"D", wherein "D", "t" and "L" are the diameter, wall thickness and length of the nozzle.
During subsequent studies of mechanically extendable stainless steel nozzles, it was noted that when a previously deployed nozzle was re-rolled into its original "stowed" configuration, its diameter had enlarged such that it did not contact the rolling guide or filler boundary employed during the previous deployment cycle and that the rolling guide performed no function during a subsequent deployment cycle. A study of this phenomena led to the conclusion that the rolling of the nozzle upon itself during the previous deployment cycle served to change the critical buckling/rolling pressure relationship of the material from which the nozzle was fabricated. It was then determined that nozzles which heretofore could not be deployed without the provision of a rolling guide or filler boundary to prevent buckling failure of a nozzle, could be successfully deployed if such nozzles were previously rolled and not subjected to a conventional annealing operation, while in their pre-rolled condition. This study subsequently led to the conclusion that the above mentioned phenomena could be used to advantage in fabricating an expulsion diaphragm having a markedly improved critical buckling pressure/rolling pressure relationship, as compared to prior diaphragm constructions.